There are many circumstances where knowing the position of one object relative to another object is important. For example, in a hospital setting, care givers need to know if an Intravenous (IV) needle has been removed from a patient's arm, or if a patient is no longer in the hospital bed, or if the patient has not moved within the hospital bed for a period of time. In another example, a security gate may recognize that an authorized person is near the security gate, and the security gate may open automatically for that authorized person, or the security gate may open for an unauthorized person if the unauthorized person is escorted by an authorized person. In yet another example, notification that two chemicals which should not be in proximity to each other are too close to each other would be extremely helpful. Various available technologies are not suitable for detecting the position of one object relative to another object. Ultrasonic technology is very expensive and requires installing new infrastructure, such as new ultrasonic receivers. Ultrasonic technology also may not work for detecting proximity in small spaces, such as the distance between an IV needle and a patient's arm. Radio Frequency IDentification (RFID) technology also has disadvantages such as positional accuracy. Therefore, there is a need to determine the position of one object relative to another that is accurate, yet low cost (for example, by using the existing infrastructure, existing security cameras, etc.), and can be implemented quickly.